Introduction to Scheduling

Personal Computer

Scheduling is simpler in personal computers because (1) there is only one active process, (2) CPU is more faster than I/O.

Process Behavior

Compute-bound: long CPU bursts and thus infrequent I/O waits. I/O-bound: short CPU bursts and thus frequent I/O waits.

race conditions

Two or more processes are reading or writing some shared data and the final result depends on who runs precisely when.

Critical Regions

mutual exclusion

Prohibit more than one process from reading and writing the shared data at the same time.

critical region

Also called critical section , the part of the program where the shared memory is accessed.

Conditions to a good solution

1. No two processes may be simultaneously inside their critical regions
2. No assumptions may be made about speeds or the number of CPUs
3. No process running outside its critical region may block other processes
4. No process should have to wait forever to enter its critical region

Thread Usage

1. Multiple activities going on at once with the ability to share an address space
2. Lighter weight than processes, easy to create and destroy.
3. Overlap activities with substantial I/O to speeding up the application.
4. Useful on systems with multiple CPUs.

Three ways to construct a server

1. Thread. Parallelism, blocking system calls.
2. Single-threaded process. No parallelism, blocking system calls.
3. Finite-state machine. Parallelism, nonblocking system calles, use interrupts to simulate thread.

Classical Thread Model

Processes are used to group resources together; threads are the entities scheduled for execution on the CPU. There are no protection betwwen threads because (1) it's impossible, and (2) it should not be nessessary.

While threads share one memory space, it takes fewer space to maintain a thread, including Program Counter, Registers, Stack and State.

pseudoparallelism

The illusion of parallelism while CPU is switching from process to process quickly.

The Process Model

process is an instance of an executing program, is the activity of a program.

If a program is running twice, it counts as two processes.

Process Creation

Processes are created when

1. System init
2. Process creation system call by a running process
3. A user request to create a new process.
4. Init of a batch job.

What is OS

1. extendes machines : providing programmers(and programs) a clean abstract set of resources instead of the messy hardware
2. resource manager : managing hardware resources

History of OS

The first digital computer was designed by Charles Babbage. Ada Lovelace was the first programmer(hired by Babbage).

1st Generation Vacuum Tubes

• The first functioning digital computer, by John Atanasoff and Clifford Berry, Iowa State University.
• Z3, Konrad Zuse, Berlin.
• Colossus, a group at Bletchey Park, England
• Mark I, Howard Aiken, Harvard
• ENIAC, William Mauchley and J. Presper Eckert, University of Pennsylvania

Vim是从vi发展出来的一个文本编辑器。代码补全、编译及错误跳转等方便编程的功能特别丰富，在程序员中被广泛使用。和Emacs并列成为类Unix系统用户最喜欢的编辑器。

文档参见：http://vimdoc.sourceforge.net/htmldoc/

中文文档：http://vimcdoc.sourceforge.net/doc/

本文介绍如何安装 Arch Linux，一个轻量级、简单的 Linux 发行版。

制作镜像并启动

在 Arch 官网下载 下载镜像（x86 和 x86_64是同一镜像）。 然后刻录 USB 安装盘：

• linux:

  dd if=/path/to/iso of=/dev/sdc  # 确认 sdc 为你的U盘
  

• windows:

  1. 下载 dd4dos
  2. dd if=/path/to/iso of="\\.\G:" # 确认G盘为你的U盘

另外，有些 U 盘就是启动不了，换一个即可。